Referring to FIGS. 1 to 3, a conventional bulb assembly of a lighting string includes a connector (1), a holder (2), and a bulb (3). Conductive plates (4) are provided in the connector (1), such that the plates (4) can contact with conductive wires (31) of the bulb (3), when the bulb (3) and the holder (2) are assembled within the connector (1). This known conductive plate (4), in order to provide effective elastic contact, is designed with an elastic plate (41), which is folded upside-down from the conductive plate (4) and is inclined. As assembly, the folded portion (42) between the conductive plate (4) and the elastic plate (41) will be easily broken under elastic compress. When the elastic plate (41) is fallen, it causes ineffective electrical contact between the conductive plate (4) and the conductive wire (31) of the bulb (3).